hdf5

[svn-r16376] Purpose: Fix a bug encountered when copying shared messages

Description: When attempting to copy an object with a message shared in its own
object header, the library attempts to protect the same object header twice.
Previously, it was possible for the object header to be protected with write
access in one or both of these protects, which would be illegal.  The library
should now always protect with read only access in this case.  The conditions
for fixing incorrect datatype versions have been made weaker to support this
change.  The version will only be corrected if the object header the datatype
is in is modified.

Tested: jam, smirom (h5committest)